1) Walton is the double of Frankenstein since he manifests the same ambition, the wish to overcome (go beyond is possible?) human limits in his travelling towards the unknown.
2)Frankenstein and his creature are complementary: they both suffer from a sense of alienation and isolation (can you say: they are alienated and isolated from society), both begin with a desire to be good but become obsessed with hate and revenge.
3) The creature stands for the scientist’s negative self and becomes a haunting presence in his life. His final rejection of the creature turns the monster into an outcast and a rebel against society.